Combined Effects Of Root Cutting And Defoliation On The Growth And Physiological Characteristics Of Quercus Variabilis Seedlings

Forests carry important ecological functions in the global ecosystem and play key roles in the carbon cycle,energy circulation and water cycle of the earth.Due to the factors such as climate change and anthropogenic disturbance,a serious threat to the sustainability of the global forest ecosystems,and the forest sustainable management through achieving the goal of promoting natural regeneration has now become has now become the focus of global attention.The seedling stage of a forest is a critical stage in the natural regeneration process,and individual seedlings at this stage are more vulnerable to the influence and restrictions of stress factors such as physical and biological factors.Therefore,studying the ability of seedlings to respond to environmental stress has important theoretical significance and practical value us to deeply understand of the self-renewal mechanism of forest ecosystems and to guide the sustainable management of forests.Roots and leaves are important nutrient storage and production organs of seedlings,which will cause losses due to physical and biological factors,which will also lead to significant changes in their growth and physiological metabolism.Quercus variabilis is widely distributed in China,and as commonly used species for vegetation restoration in China,it is often vulnerable to physical and biological factors during the seedling stage,which affects its survival and growth strategies.The growth and physiological mechanisms of how Q.variabilis seedlings to respond to the degree of root and leaf loss is currently unclear.Therefore,this study selected first-year Q.variabilis seedlings as research objects,and using defoliation and root cutting intensity to simulate the degree of loss of leaf and root.Three root cutting(0,1/3 and 1/2)and three defoliation(0,1/3 and 1/2)interactive treatments were set,for a total of nine treatments,including whole root whole leaf,whole root defoliation 1/3,whole root defoliation 1/2,root cutting 1/3 whole leaf,root cutting 1/2 whole leaf,root cutting 1/3 defoliation 1/3,root cutting 1/2 defoliation 1/3,root cutting 1/3 defoliation 1/2 and root cutting 1/2 defoliation 1/2 treatments.By analyzing the effects of different loss degrees of root and leaf on the growth physiological characteristics and interrelationships of Q.variabilis seedlings,it is clarified to clarify the growing physiological mechanism of loss of root and leaf.The main results of this study were obtained as follows:(1)Root loss inhibited the growth of Q.variabilis seedlings.Both height and ground diameter of Q.variabilis seedlings showed a decreasing trend with increasing root loss.Specifically,the height of Q.variabilis seedlings with 1/3 root cutting and1/2 root cutting was significantly lower than that of CK,and the height after 1/3 root cutting was higher than that of 1/2 root cutting.It also was found that light defoliation promoted seedling height growth,while heavy defoliation inhibited Q.variabilis seedling growth.The height of Q.variabilis seedlings in the 1/3 defoliation was significantly higher than CK,while the height of seedlings in the 1/2 defoliation was lower than CK.Root loss altered the biomass allocation pattern of Q.variabilis seedlings to the below-ground portion of the biomass,while leaf loss had no significant effect on the biomass of both above and below ground portions of Q.variabilis seedlings.(2)Root loss significantly inhibited net photosynthetic rate and stomatal conductance of leaves of Q.variabilis seedlings.The net photosynthetic rate and leaf stomatal conductance of Q.variabilis seedlings decreased with the increase of root loss;while leaf loss promoted the net photosynthetic rate and stomatal conductance of Q.variabilis seedlings to some extent,and the net photosynthetic rate and stomatal conductance of 1/3 defoliated were greater than 1/2 defoliated,and were higher than those of non-defoliated Q.variabilis seedlings.(3)Root loss reduced morphological indicators such as primary root length,total root surface area,volume and density of Q.variabilis seedlings.And the primary root length,root volume and root density of Q.variabilis seedlings gradually decreased as the degree of root loss increased.The leaf loss only affected the root surface area of Q.variabilis seedlings and had no significant effect on other root morphological parameters.The 1/3 defoliation significantly promoted the root surface area growth of Q.variabilis seedlings while the 1/2 defoliation inhibited the root surface area.(4)After root damage,Q.variabilis is able to adjust the dynamics of NSC content in various parts of its body to ensure the normal survival and growth of seedlings.The NSC content in the roots of Q.variabilis seedlings with 1/3 root cutting treatment was higher than that of CK,while that of Q.variabilis with 1/2 root cutting was lower than that of CK;leaf loss reduced the starch and NSC content in the roots,stems and leaves of Q.variabilis seedlings,but increased the soluble sugar content in the leaves.Both starch and NSC contents in roots,stems and leaves of Q.variabilis seedlings were affected with the increase of leaf loss.